docs: def contribute_to_class(model_class, name='slots', descriptor=None):
      """
      Function that adds a description to a model Class.
  
      :param model_class: The model class the descriptor is to be added
      to.
      :param name: The attribute name the descriptor will be assigned to.
      :param descriptor: The descriptor instance to be used. If none is
      specified it will default to
      ``icekit.plugins.descriptors.PlaceholderDescriptor``.
      :return: True
      """
      rel_obj = descriptor or PlaceholderDescriptor()
      rel_obj.contribute_to_class(model_class, name)
      setattr(model_class, name, rel_obj)
      return True